Static liquid piston compressor and expander systems and methods for same

ABSTRACT

A liquid piston system includes a liquid piston compressor/expander assembly and a drive mechanism. The liquid piston compressor/expander assembly includes a reciprocating cylinder coupled with the drive mechanism and a static liquid piston received in the cylinder cavity. The static liquid piston includes a piston face configured to carry liquid piston fluid. The reciprocating cylinder is configured to move relative to the static liquid piston between contracted and expanded positions. In a compressor, at the expanded position the cylinder head is withdrawn from liquid piston fluid and the cylinder cavity is filled with the compressible fluid. In the contracted position the cylinder head of the reciprocating cylinder is near the liquid piston fluid and the compressible fluid is compressed. With an expander, in the contracted position the compressible fluid is introduced to the cylinder cavity and the expanding compressible fluid moves the reciprocating cylinder to the expanded position.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under award number EFRI-1038294 awarded by the National Science Foundation. The government has certain rights in this invention.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawings that form a part of this document: Copyright Regents of the University of Minnesota, Minneapolis, Minn. All Rights Reserved.

TECHNICAL FIELD

This document pertains generally, but not by way of limitation, to gas compressors and expanders.

BACKGROUND

Mechanical compressors and expanders (e.g., engines, pumps or the like) compress or expand a compressible fluid for a variety of functions. With compressors the fluid is compressed to compactly store the fluid under high pressure for later use (e.g., compressed air for pneumatic tools, energy storage with wind turbines or the like). Mechanical compressors and expanders use one or more of cylinder and piston arrangements, screws or the like to compress or expand the fluid. A seal is created between the moving piston or screws and a wall (e.g., a cylinder wall or chamber wall).

Liquid pistons are used in some examples as compressors or expanders. The liquid piston fluid is formed along the face of a driven piston and provides an interface with the compressible fluid (e.g., it is between the driven piston face and the compressible fluid). The liquid piston provides a seal between the cylinder and the mechanical (solid) piston. As a compressor, the liquid piston moves relative to the cylinder to compress the compressible fluid. Conversely, as an expander (engine, pump or the like) the compressible fluid moves the liquid piston relative to the cylinder to generate power including rotation of a shaft, impeller, fan or the like.

Overview

The present inventors have recognized, among other things, that a problem to be solved can include overcoming disturbances at the interface of the compressible fluid and the liquid piston fluid. For instance, when a liquid piston operates at one or more of relatively high frequencies or accelerations (including decelerations) the liquid piston fluid is readily disturbed by the movement of the piston In some examples the liquid piston fluid is splashed along the cylinder walls and upwardly into the cylinder chamber. The splashed liquid piston fluid, in an example, is withdrawn from the cylinder in place of the compressed or expanded compressible fluid and thereby negatively affects the system efficiency. Additionally, the extracted liquid piston fluid decreases the volume of the liquid piston while the remaining liquid piston fluid is infiltrated with compressible fluid bubbles. Accordingly the cylinder cavity volume increases throughout the duty cycle. The change in volume negatively affects the compression ratio of a compressor and power output of an engine.

In an example, the present subject matter can provide a solution to this problem, such as by providing a compressor (or expander) assembly having a static liquid piston and moving cylinder. The static liquid piston includes liquid piston fluid statically held throughout operation of the compressor assembly. The cylinder moves relative to the static liquid piston (e.g., is driven by one or more of a linkage, cam follower assembly or the like). Because the liquid piston fluid is static the compressor assembly is operated at higher frequencies (e.g., one or more of greater than 2.2 Hz or with cylinder deceleration of one gravity or greater) and with greater efficiency without disturbance of the compressor fluid and liquid piston fluid interface. Shearing forces generated by the cylinder with the liquid piston fluid (and corresponding retention of the fluid along the cylinder walls) are optionally minimized with one or more of phobic coatings, or overcome by ferrofluid liquid piston fluids or the like, as described herein.

Further, because the liquid piston is static the liquid piston fluid is readily cycled through a heat transfer circuit to cool the liquid piston fluid during operation. In the example of a compressor, the liquid piston fluid extracts heat from the compressible fluid and the compressible fluid experiences isothermal compression (e.g., including near isothermal compression) and minimizes the input work of the compressor drive mechanism. Typically the input work of the drive mechanism is greater to overcome the opposed increase in energy created by the rising pressure and rising temperature of the compressed fluid during compression. In one example, the compressor assembly and liquid piston compressor system including the same described herein achieves efficiencies of around 94 percent relative to adiabatic compressors that have efficiencies of around 65 percent.

The present inventors have recognized, among other things, that another problem to be solved can include decreasing retention of liquid piston fluid within the cylinder during the expansion portion of the piston stroke. In some examples (described herein) the cylinder cavity is at least partially filled with a porous media. During compression of a compressible fluid the fluid is compressed in the interstitial locations within the porous media. Compression heats the compressible fluid and the porous media extracts the heat from the compressible fluid. The liquid piston fluid fills the interstitial locations and extracts the heat from the porous media. The heated liquid piston fluid is then cycled through a heat exchanger to exhaust the extracted heat. Accordingly, the compressible fluid is compressed in an isothermal fashion with little to no temperature change between compressed and uncompressed states (e.g., including near isothermal with a temperature increase of a few degrees or pockets of high temperature compressed fluid in an overall near isothermal volume of compressed fluid).

Retention of the liquid piston fluid within the porous media frustrates the transfer of heat. Further, retention of the liquid piston fluid fills the cylinder cavity, traps compressible fluid in the interstitial locations and accordingly decreases the compression ratio of a compressor and its corresponding efficiency (or efficiency of an engine, pump or the like). Retention of the liquid piston fluid may also occur along the cylinder walls because of fluid shearing forces (e.g., viscoelastic properties of the liquid piston fluid) and at high operating frequencies causing lateral splashing along the cylinder head.

In an example, the present subject matter can provide a solution to this problem, such as by providing a compressor (or expander) that uses phobic coatings (e.g., hydrophobic, oleophobic, or lipophobic coatings) to ensure the liquid piston fluid remains with the piston face as the cylinder is withdrawn (e.g., and the cylinder cavity expands). In another example, the liquid piston fluid includes a ferrofluid that is biased to remain along the piston face (and thereby withdraws from porous media during expansion) by a retention magnet (e.g., magnet, electromagnet, electromagnetic field generator or the like) for instance a retention magnet positioned within the piston face.

This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1A is a perspective view of one example of a static liquid piston compressor.

FIG. 1B is a perspective view of one example of a static liquid piston expander.

FIG. 2 is a cross sectional schematic view of one example of a static liquid piston assembly.

FIG. 3 is a cross sectional schematic view of another example of a static liquid piston assembly having a central rod.

FIG. 4A is a schematic view of the static liquid piston assembly of FIG. 3 filling with a compressible fluid prior to compression.

FIG. 4B is a schematic view of the static liquid piston assembly of FIG. 4A compressing the compressible fluid.

FIG. 5A is a schematic view of the static liquid piston assembly of FIG. 3 prior to expansion of the compressible fluid.

FIG. 5B is a schematic view of the static liquid piston assembly of FIG. 5A with the compressible fluid expanding.

FIG. 6 is a detailed cross sectional view of a liquid piston including a disturbed liquid piston fluid interface.

FIG. 7 is a schematic view of another example of a static liquid piston assembly including a ferrofluid anchor system.

FIG. 8 is a block diagram showing one example of a method of using a static liquid piston assembly.

DETAILED DESCRIPTION

When rapidly compressing a gas with minimal heat transfer, significant energy is converted into increasing the gas temperature. When the compressed gas cools at constant pressure in a storage reservoir, the potential energy of the gas decreases, reducing the efficiency of the overall cycle. By increasing the heat transfer during compression to near isothermal conditions (e.g., isothermally compressing the compressible fluid), the energy required to compress the same mass of gas to the same final, cooled state decreases. The reduction in work done on the gas improves the efficiency of the gas compression or expansion process and enables efficient energy storage through gas compression.

In some examples, current applications involving compression and expansion of gases, such as air compressors, internal and external combustion engines, and air motors, utilize mechanical methods of sealing the gas while changing the volume. These mechanical compression and expansion methods, such as the reciprocating piston, screw compressors, and vane compressors, provide poor heat transfer between the mechanical system and the compressible gas. The heat transfer is poor in these machines due to the high frequency operation and the practical geometry requirements that dictate a poor surface area to volume ratio. There have been efforts to improve the surface area to volume ratio by using a small diameter cylinder with a long stroke or a large diameter cylinder with a short stroke. Attempts to improve this ratio have also included placing protrusions on the moving piston that slide into cavities in the cylinder endplate, increasing the surface area of the compression space.

Beyond poor heat transfer, mechanical methods of compressing and expanding gases suffer from a trade-off between gas leakage and high sealing friction. Seal design has been an active area of research, with work ranging from attempting to minimize friction through seal geometry, analyzing seal friction and power loss associated with various lubricants, experimentally determining the life of seals before failure, and analyzing the leakage of various seal designs. There has been work done specifically on internal combustion engine seals, including analyzing friction and sealing for various piston ring designs. Balancing seal friction with leakage is an issue for other mechanical compression and expansion methods as well, such as scroll compressors, screw compressors, and vane compressors.

An alternative to a mechanical piston, a liquid piston (as discussed herein) is used to directly compress or expand a gas in a fixed volume chamber. The liquid piston eliminates the mechanical sliding seals associated with kinematic compressors. By replacing these seals with a liquid column, gas leakage is eliminated and the sliding (mechanical) friction is replaced with viscous fluid forces.

Because the liquid piston (e.g., liquid piston fluid) conforms the liquid pistons fluid flows through an irregularly shaped gas chamber. Accordingly, the surface area to volume ratio of the chamber is dramatically increased by adding a porous media in some examples. Porous media options include, but are not limited to cylinders, fins, meshes, one or more of tubes, posts, fins, interlaced tubes, interlaced posts, interlaced fins, tilted interrupted plates, profiled cylinder cavity walls, metallic foam or wire mesh or a variety of other geometries. During the compression stroke, the compressed gas transfers heat to the porous media. The porous media is a heat sink (or in the case of an expander heat adder) isothermalizing the compression. As the liquid piston fluid displaces the gas, it fills the interstitial locations within the porous media and contacts the surface area elements of the porous media and absorbs heat. During retraction of the liquid piston, the heated liquid piston fluid is exhausted to the reservoir. Optionally, the heated liquid piston fluid is cycled through a heat exchanger in preparation for the next cycle. The cycle then repeats.

A challenge of liquid piston systems is the stability of the liquid-gas interface during acceleration (and deceleration) of the liquid piston. Many researchers have studied surface stability between two fluids of different densities. If the acceleration opposing gravity of the higher density fluid (e.g., the liquid piston fluid) exceeds gravitational acceleration, the interface between the liquid and the gas becomes unstable, resulting in gas bubbles penetrating the liquid and liquid drops ejected into the gas. Minimizing surface instability limits the operating frequency of a liquid piston machine, and accordingly limits the power density. In a CFD study of liquid piston gas compression, the inventor found geometry dependent instability at accelerations as low as −0.5 g. limiting the operating frequency of a liquid piston with a sinusoidal stroke of 5 cm to 2.2 Hz.

To exploit the sealing and heat transfer benefits of the liquid piston with porous heat transfer media, while avoiding the frequency limitations required to maintain a cohesive gas-liquid interface, an inverted liquid piston is described herein that includes a reciprocating piston and static liquid piston. In the inverted liquid piston compressor and expander examples described herein the cylinder head, reciprocating cylinder, and the porous heat transfer media move relative to a stationary liquid column (e.g., a static liquid piston fluid). As the high-density fluid, the liquid piston fluid, does not accelerate due to reciprocating cylinder movement and accordingly the inverted liquid piston does not incur Rayleigh-Taylor interface instability. Furthermore, by moving the cylinder walls, the liquid sealing interface remains between the cylinder and the static liquid piston fluid in the liquid region of the assembly, allowing much lower friction and leakage compared to a mechanical seals in the gas region.

The displacement of the reciprocating cylinder and the cylinder cavity is conducted in a variety of ways, including, but not limited to, a crank-slider linkage with an adjustable linkage to create variable displacement, similar to other examples of hydraulic pumps, with a cam-follower, or by other means. The drive mechanism for displacing the reciprocating cylinder and the cylinder cavity is optionally above the cylinder and connected to the cylinder head, as shown, or is mounted below the chamber and connected to the sides of the reciprocating cylinder.

Alternatively, a central rod is connected to the center of the top cap (e.g., the cylinder head) and passes through a bearing and seal in the base endcap (e.g., the piston) to a connection with the actuating mechanism as shown herein. Using the central rod as a linear bearing instead of the cylinder is advantageous because the small diameter of the central rod results in a large bearing ratio with a reasonably short bearing length. The bearing ratio of a cylindrical linear bearing is defined as the length of the bearing divided by the diameter.

Transferring gas in and out of the inverted liquid piston system (e.g., the cylinder cavity) is achieved in a variety of ways. Two possibilities for compressible gas transfer include connecting one or more flexible conduits (e.g., ports) to the moving cylinder head, reciprocating cylinder body, the central rod or by passing a fixed conduit through the piston face with an opening just above the liquid piston fluid level. In the case of an air compressor, check valves are mounted directly to the cylinder head or the piston face (e.g., at the ports) and connected to the inflow and outflow (storage) reservoirs with flexible conduits. The inertial forces from the moving reciprocating cylinder acceleration assist the check valves in opening and closing with corresponding timing to the cycle. In other words, the inertial forces on the moving elements of the check valves (valve flapper, rod and springs) are in the upward direction at top-dead-center (expanded position), which would assist the pressure valve to open and the intake valve to close while the converse occurs at bottom-dead-center (contracted position).

In addition to operation as a gas compressor or expander, the inverted liquid piston system is also used as a heat engine to create near-isothermal compression and expansion. One application is a liquid piston Stirling engine.

Two challenges are introduced by the incorporation of porous media into the cylinder cavity of the inverted liquid piston compressor. The first challenge is the no-slip boundary condition along the cylinder walls and in the porous media, which acts to draw the liquid piston upward as the chamber moves up and pushes gas down into the liquid as the chamber moves down. At higher frequencies this movement may yield undesired mixing and splashing of the two phases (e.g., compressible fluid and liquid piston fluid). The second challenge is derived from the combined action of surface wetting adhesive forces between the liquid phase (liquid piston fluid) and the solid porous material (of the porous heat transfer media) and cohesive forces within the liquid piston fluid prompting it to coalesce into films on the wetted surface of the media. If the pore size is too small these films occlude and trap gas bubbles within the porous media.

These issues are addressed in one example by applying a phobic coating to the cylinder and porous media which facilitates the maintenance of a thin gas layer at the surface of the porous media. In another example, the porous media is absent from the liquid piston system to avoid wetting and gas retention. In such an example, heat transfer to the static liquid piston fluid is optionally enhanced with liquid spray to create atomized liquid particles (e.g., droplets) with a high surface area. Once these droplets contact a surface including one of the cylinder wall or the static liquid piston fluid they drain and become part of the stationary liquid piston. The liquid piston fluid is thereby heated and an optional heat exchanger extracts the heat and recycles the liquid piston fluid.

In another example, the liquid piston assemblies described herein use a ferrofluid as the liquid piston fluid. A ferrofluid is a three component magnetic fluid such as a colloid consisting of subdomain magnetic particles optionally coated with a surfactant and suspended within a carrier liquid. The surfactant is matched to the carrier fluid such that it overcomes the attractive van der Waals and magnetic forces between the particles and prevents agglomeration. When exposed to an external magnetic field, for instance from the retention magnet discussed herein, the ferrofluid experiences a body force directed along the gradient toward the region of highest flux (e.g., across the piston face).

By using a ferrofluid for the liquid piston and generating a magnetic field at the base of the chamber with a retention magnet including one or more of a permanent magnet (neodymium magnet), electro-magnet or the like (shown herein) a downward biasing force is applied to the liquid piston fluid. The magnetic force balances the induced forces on the liquid from the no-slip boundary condition of the moving walls and porous heat transfer media and stabilizes the interface of the compressible gas and the liquid piston fluid. This effectively retains the liquid piston fluid along the piston face and facilitates increasing one or more of the maximum frequency of operation or acceleration of the cylinder for the liquid piston systems described herein while minimizing splashing and mixing between the fluid phases.

In addition to allowing the liquid piston system to operate at greater frequencies, the increased downward body force exerted on the liquid piston overcomes greater adhesive and cohesive forces that otherwise tend to form occluded air bubbles within the porous heat transfer media. Accordingly, the minimum allowable spacing between features of the porous material (e.g., size of the interstitial locations) is reduced and a greater surface area to volume ratio is realized in the cylinder cavity. Larger surface area to volume ratios further enhance heat transfer to and from the compressible fluid, allowing the systems to compress or expand higher mass flow rates of gas at near isothermal conditions. This facilitates operation of the inverted liquid piston systems described herein at high power densities (e.g., efficiently).

Further, the liquid piston ferrofluid provides sealing and bearing enhancements. For instance, the liquid piston ferrofluid is engineered to have low viscosity and long life for use in high performance seals. When used between bearing surfaces, the hydrocarbon base of a ferrofluid acts as a lubricant, and the attraction of the fluid toward the region of highest magnet flux is leveraged in the design to aid in the development of full film lubrication. In one example, the retention magnet (including one or more retention magnets) are positioned around the perimeter of the piston face to ensure retention of a portion of the liquid piston ferrofluid at the cylinder and liquid piston interface. The bulk properties of the ferrofluid, such as viscosity and saturation magnetization are optionally influenced by varying its individual constituents. In this manner a liquid piston ferrofluid with an appropriate profile of characteristics is provided to satisfy the requirements of the inverted liquid piston system.

FIG. 1A shows one example of a static liquid piston system 100. As shown, the static liquid piston system 100 includes one or more static liquid piston assemblies 102 coupled with an input or output device, for instance, the input device 104 shown in FIG. 1A. In the example shown, the input device 104 includes a crank shaft having one or more shaft joints 122 connecting the static liquid piston assemblies 102 to the input device 104. In one example, the input device 104 is operated by an input 106, for instance, a rotational input to rotate the input device 104 and correspondingly rotate the shaft joints 122. Rotation of the shaft joints 122 moves connecting rods 120 coupled with each of the cylinders 108 of the static liquid piston assemblies 102. For instance, as shown in FIG. 1A, the connecting rods 120 are coupled with the cylinders 108 by way of cylinder joints 124 (e.g., at the cylinder heads 126).

As further shown in FIG. 1A, rotation of the input device 104 (e.g., by the input 106) correspondingly moves the connecting rods 120 and thereby reciprocates the cylinders 108 relative to the pistons 110. That is to say, as shown in FIG. 1A, the static liquid piston assemblies 102 each include a static piston 110 and a moveable cylinder 108 that reciprocates relative to the pistons 110. As further shown in FIG. 1A, each of the static pistons 110 further includes a static liquid piston 116 for each of the pistons 110. In one example, a piston face 112 of the piston 110 in combination with the liquid piston fluid 114 forms the static liquid piston 116 of each of the assemblies 102. As further shown in FIG. 1A, each of the static liquid pistons 116 includes a liquid piston interface 118, for instance, an upper surface of the static liquid piston 116. The liquid piston interface 118 is the surface of the static liquid piston 116 facing a compressible fluid and the cylinder head 126 within each of the cylinders 108 of the static liquid piston assemblies 102.

In one example, the liquid piston fluid 114 is an incompressible fluid including, but not limited to, water, oil glycol based fluids or the like. The liquid piston fluid 114 conforms to the shape of the cylinder 108 and thereby provides a continuous unbroken seal between the static liquid piston 116 and the cylinder 108. Accordingly, tight gaskets and the like that otherwise frictionally resist movement of the cylinder 108 are absent or are provided with greater tolerances to facilitate the ready movement of the cylinder 108 relative to the piston 110. In another example, the liquid piston fluid 114 includes an incompressible fluid including, but not limited to, water an oil or the like. The incompressible fluid provides a robust liquid piston interface 118 with the compressible fluids to facilitate one or more of compression or expansion. Accordingly, with reciprocation of the cylinder 108 relative to the piston 110 compression of the compressible fluid within the cylinder 108 is readily achieved. In a similar manner, where the static liquid piston system 100 is used as an expander (e.g., as an engine) the liquid piston interface 118 of the static liquid piston 116 provides the interface with the compressible fluid within each of the cylinders 108. As further shown in FIG. 1A, in the arrangement of the static liquid piston system 100 the pistons 110 are in a static configuration relative to the cylinders 108. As previously described herein, the liquid piston fluid 114 in this example is provided along the piston faces 112 of each of the pistons 110. Because the cylinders 108 reciprocate relative to the pistons 110, the liquid piston fluid 114 remains in a substantially static position on the piston 110 (e.g., along the piston face 112). Accordingly, with movement of the cylinder 108 the liquid piston fluid 114 remains stationary. Disturbances in the liquid piston fluid 114 are thereby minimized.

Further, in some examples the liquid piston fluid 114 includes a lubricant, such as an oil whether petroleum based, synthetic or the like or other fluid configured to lubricate the respective sliding interfaces between the pistons 110 and the cylinders 108. Because the liquid piston fluid 114 is substantially stationary along the piston face 112 the liquid piston fluid is reliably distributed across the face including along the edges of the face where the cylinder wall slides there along. The liquid piston fluid 114 lubricates this interface while at the same time providing the liquid piston interface 118 to the compressible fluid.

Because the static liquid piston 116 is static relative to the remainder of the static liquid piston assembly 102, including the cylinder 108, each of the static liquid piston assemblies 102 is operated at accelerations and decelerations greater than accelerations or decelerations achievable with a liquid piston including a moving piston (with correspondingly moving liquid piston fluid). For instance, the system 100 shown in FIG. 1A is, in one example, operated (e.g., at 2.2 hertz) with accelerations and corresponding decelerations of one (1) gravity or more (e.g., 1-10 gravities or the like). The cylinders 108 reciprocate (at frequencies including, but not limited to, 1, 2, 2.2, 3 Hz or more or the like) to match the relatively rapid rotation of the input device 104. Even at the relatively high accelerations achievable with reciprocation the liquid piston interface 118 of the static liquid piston 116 is maintained in a substantially undisturbed fashion. The maintenance of the liquid piston interface 118 and corresponding operation at higher accelerations (and decelerations) increases the efficiency and output (e.g., power, work or the like) of the static liquid piston system 100. As further described herein, the static liquid piston assemblies 102 optionally include one or more features to shed liquid piston fluid in contact with various features of the assemblies 102. In one example, the systems described are operated at one or more frequencies achievable with the static liquid piston arrangements described herein. For instance, large output expanders and compressors are operable at around 1 Hz or greater, moderate output expanders and compressors are operable at around 10 Hz or greater, and small output expanders and compressors are operable at around 50 Hz or greater.

In one example, one or more of the cylinders 108, porous media within cylinder cavities or the like include phobic coatings to readily shed the liquid piston fluid during operation of the static liquid piston assemblies 102. For instance, where the liquid piston fluid 114 includes water, one or more of the cylinder 108, the porous media or the like include hydrophobic coatings configured to readily shed the liquid piston fluid 114 from interfaces along the cylinder walls, the porous media or the like. Shedding of the liquid piston fluid 114 maintains the fluid along the piston face 112 and accordingly assists in maintaining the liquid piston interface 118 while minimizing mixing with the compressible fluid, formation of bubbles in the liquid piston fluid or splashing of the liquid piston fluid or the like even with the liquid piston fluid infiltrating and exiting a porous media with movement of the cylinders 108.

In another example (described herein), one or more anchoring features, for instance, magnets or the like, are used with a liquid piston fluid 114 including ferrous particles, such as a ferrofluid. The one or more magnets anchor the liquid piston ferrofluid along the piston face 112 and thereby minimize the retention of liquid piston fluid 114 within porous media or along walls of the cylinders 108. The retention of the liquid piston fluid 114 at the static piston 110 (e.g., along the piston face 112) minimizes splashing of the liquid piston fluid 114, infiltration of the compressible fluid into the fluid 114, and entrapment of either or both of the liquid piston fluid 114 or the compressible fluid within a porous media. Accordingly, the efficiency, power, work or the like of the static liquid piston system 110 is enhanced.

FIG. 1B shows another example of a static liquid piston system 101. In the example shown in FIG. 1B, the system 101 includes an expander system, such as an engine. As shown, each of the static liquid piston assemblies 102 includes a static piston 110 and a moving cylinder 108. The static pistons 110 and the moving cylinders 108 in FIG. 1B are similar in at least some regards to the corresponding pistons and cylinders shown in FIG. 1A. Each of the cylinders 108 is coupled with an output device 105, for instance an output device by way of the connecting rods 120. The output device 105 is in another example coupled with an output 128 including, but not limited to a generator, mechanical output, transmission or the like

As shown in FIG. 1B, the static liquid piston assembly 102 on the right of the system 101 includes the cylinder 108 beginning upward travel relative to the cylinder 108 shown to the left. In an example, a compressible fluid, for instance, compressed air, nitrogen or the like, is introduced into the cylinder 108 by way of one or more one-way valves. The introduction of the compressed fluid into the static liquid piston assembly drives the cylinder 108 upwardly relative to the static piston 110. The movement of the cylinder 108 is transmitted to the output device 105 by way of the connecting rod 120. The rotation provided to the output device 105 is, in one example, transmitted to the other cylinder 108 of the second static liquid piston assembly 102 (of the system 101). The cylinder 108 of the second assembly 102 thereby descends into an orientation similar to the rightmost static liquid piston assembly 102 and is then ready to receive the compressible fluid therein. As with the static liquid piston system 100, including a compressor shown in FIG. 1A, the static liquid piston system 101 shown in FIG. 1B uses the liquid piston interface 118 of each of the static liquid pistons 116 of the assemblies 102 to provide a robust static interface with the compressible fluid so that reception of the compressible fluid within the cylinders 108 moves the cylinders relative to the piston 110. As previously described, the static liquid piston, for instance provided by the liquid piston fluid 114 along each of the piston faces 112, provides a conforming seal between the cavity of the cylinder 108 and the interface of the cylinder walls with the piston 110. Accordingly, the static liquid piston 116 minimizes leaking, for instance, of the compressible fluid around or through the interface between the piston 110 and the cylinders 108. Instead, a tight conforming seal is provided by the liquid piston fluid 114 to ensure an efficient expansion (or compression) of the compressible fluid within the static liquid piston assembly 102. Gaskets, such as O-rings or the like, are thereby minimized, for instance with increased tolerances to decrease friction between the cylinders 108 and the pistons 110.

In a similar manner, the static liquid piston system 100 shown in FIG. 1A provides a conforming seal with the liquid piston fluid 114 along the piston face 112. In this example, the input of the input device 104, for instance, to each of the connecting rods 120, compresses a compressible fluid within each of the static liquid piston assemblies 102. A conforming seal provided by the static liquid piston 116 substantially minimizes (e.g., minimizes or eliminates) the leaking of the compressible fluid between the interface of the cylinder walls and the piston 110 while at the same time decreasing friction therebetween. In the example shown in FIG. 1A, the cylinder 108 to the left of the system 100 is filled with compressible fluid on the cylinder upstroke. As the input device 104 begins the down stroke of the cylinder 108 the static liquid piston 116, including the liquid piston fluid 114 and the piston face 112, cooperate to provide a sealed interface between the piston 110 and the cylinder 108 to minimize leaking of the compressible fluid between the cylinder 108 and the piston 110. Instead, a sealed cavity is provided within the cylinder 108 to ensure an efficient compression of the compressible fluid therein during operation of the static liquid piston system 100.

FIG. 2 shows a cross-sectional view of one example of a static liquid piston assembly such as the static liquid piston assembly 102 shown previously in FIGS. 1A, 1B. As shown and as previously described, the cylinder 108 is coupled with the drive, for instance, the input device 104 such as a crank shaft. For instance, a connecting rod 120 coupled with the input device 104 at a shaft joint 122 is also coupled with the cylinder 108 with a cylinder joint 124. As shown in FIG. 2 and as previously shown in FIGS. 1A, 1B, the cylinder joint 124 is in turn coupled with the cylinder head 126. Rotation of the input device 104 moves the connecting rod 120 and the cylinder 108 in a reciprocating fashion relative to the piston 110. In one example, where the crank shaft is an input device 104 previously described herein, rotation of the crank shaft compresses a compressible fluid within the static liquid piston assembly 102. In another example, the shaft includes the output device 105, for instance shown in FIG. 1B. A compressible gas is introduced to the cylinder 108 while compressed. The expansion of the compressed gas drives the cylinder 108 relative to the static piston 110 and moves the connecting rod 120 to rotate the output device 105.

The interior of the cylinder 108 including, for instance, a cylinder cavity 202, is shown in FIG. 2. In the example, the liquid piston fluid 114 is shown in a static orientation along the piston face 112. As previously described herein, the cylinder 108 of the static liquid piston assembly 102 moves relative to the piston 110 and the liquid piston fluid 114. The static liquid piston 116 including, for instance, the liquid piston fluid 114 and the piston face 112, is accordingly stationary relative to the moving cylinder 108. The compressible fluid 200 within the cylinder cavity 202 is compressed or expanded (depending on the function of the static liquid piston assembly 102) according to movement of the cylinder 108. The liquid piston fluid 114 provides a liquid piston interface 118 as previously described herein engaged with the compressible fluid 200. The liquid piston interface 118 cooperates with the cylinder 108 to thereby compress or expand the compressible fluid 200.

Further, because the liquid piston fluid 114 resides along the piston face 112 and the piston 110 is static, the liquid piston fluid 114 is similarly static (e.g., stationary). Stated another way, the cylinder 108 moves with respect to the liquid piston fluid 114 and thereby facilitates the maintenance of the liquid piston interface 118 in an undisturbed fashion (e.g., with limited or no disturbance) during reciprocation of the cylinder 108. Accordingly, the compressible fluid 200 remains separated from the liquid piston fluid 114 (e.g., is not mixed) and the efficiency of the static liquid piston assembly 102 is maintained. As will be described herein, in one example, the cylinder 108 including, for instance the cylinder walls 204 and a porous media optionally provided in the cylinder cavity 202, are provided with a phobic coating configured to facilitate the shedding of the liquid piston fluid 114 during reciprocation of the cylinder 108 relative to the piston 110. The phobic coating enhances the retention of the liquid piston fluid 114 along the piston face 112 and minimizes adhesion of the fluid 114, for instance, along the cylinder wall 204 and the porous media or the like. The cylinder 108 is thereby driven or drives the input device 104 or output drive 105, respectively, at a higher accelerations (and decelerations), for instance around one (1) gravity or more without appreciably disturbing the liquid piston fluid 114. Accordingly, mixing of the liquid piston fluid 114 and the compressible fluid 200, retention of the fluid 114 along surfaces other than the piston face 112 or the like is thereby minimized and the efficiency and effectiveness (e.g., output such as work, power, compressed fluid) of the static liquid piston assembly 102 is increased.

As further shown in FIG. 2, the liquid piston fluid 114 is in a conforming shape relative to the cylinder wall 204 and the piston face 112. That is to say, the liquid piston fluid 114 automatically conforms to the shape of the cylinder wall 204 and the piston face 112. As the cylinder 108 reciprocates relative to the piston 110, the liquid piston fluid 114 is static (e.g., with minimal or limited disturbances) and held stationary relative to the cylinder wall 204. That is to say, the liquid piston fluid 114 is sheared by the cylinder 108 as it moves along the liquid piston fluid 114 in a reciprocating fashion shown, for instance corresponding to the up and down arrows in FIG. 2. Additionally, because the liquid piston fluid 114 is maintained along the piston face 112 (as described herein), a consistent and reliable seal is provided between the compressible fluid 200 and the interface between the cylinder wall 204 and the piston 110. Accordingly, the compressible fluid 200 is not able to leak between the cylinder 108 and the piston 110.

FIG. 3 shows a cross-sectional view of another example of a static liquid piston assembly 300. In the example shown in FIG. 3, the cylinder 304 is moveable relative to the piston 302 as previously described in other embodiments herein. A cylinder rod 308 extends from the cylinder head 306 through the interior of the cylinder 304 and through the piston 302. As previously described, the piston 302 is a stationary feature within the static liquid piston assembly 300. In one example, the cylinder rod 308 extending through the piston 302 is guided and supported, for instance, against lateral movement, binding and the like by the slidable engagement of the cylinder rod 308 along the corresponding surfaces of the piston 302. In a similar manner to the interface between the cylinder 304 and the piston 302, the liquid piston fluid 324 provides a sealed (and lubricated) interface between the cylinder rod 308 and the piston 302. In another example, the interface between the piston 302 and the cylinder rod 308 includes gaskets, such as O-rings. The gaskets alone or in combination with the liquid piston fluid 324 are configured to provide a fluid tight seal between the cylinder rod 308 and the piston 302. The cylinder rod 308 is, in one example, reciprocated, for instance, with one or more of a crank shaft, cam system or the like to accordingly move the cylinder rod 308 and the associated cylinder 304 relative to the piston 302 (including the static liquid piston 328 including the liquid piston fluid 324 provided along the piston face 326).

FIG. 3 further shows an inflow source 312 and an outflow source 314 in communication with the static liquid piston assembly 300. In one example, the inflow source 312 is in communication with the interior of the static liquid piston assembly 300 by way of an inflow passage 316 and one or more inflow ports 334 provided above the liquid piston interface 330. Because the one or more inflow ports 334 (as well as the one or more outflow ports 336) are provided above the liquid piston interface 330, the inflow and outflow ports 334, 336 are not fouled during operation of the static liquid piston assembly 300. Referring again to FIG. 3, the outflow source 314 is similarly connected to the outflow port 336, for instance, by an outflow passage 318.

Optionally, one or more unidirectional valves 342, such as check valves, are provided between the inflow source 312 and the inflow port 334 and between the outflow source 314 and the outflow port 336 to ensure unidirectional movement of the compressible fluid into and out of the static liquid piston assembly 300. In one example, the unidirectional valves 342 cooperate with operation of the static liquid piston assembly 300. For instance, expanding movement of the cylinder 304 relative to the piston 302 (whether in compression or expansion) allows the admission of the compressible fluid from the inflow source 312 into the cylinder 304 (e.g., filling of the cylinder during expansion or filling prior to compression) through the unidirectional valve associated with the inflow passage 316. While filling the unidirectional valve for the outflow passage 318 remains closed to prevent back flow. Contracting movement of the cylinder (whether in compression or exhaustion of expanded fluid) conversely closes the unidirectional valve 342 associated with the inflow passage 316. The unidirectional valve 342 associated with the outflow passage 318 is opened during exhausting of the (expanded) compressible fluid and selectively opened during compression of the compressible fluid (e.g., with a valve cam shaft, offsetting of a valve spring bias according to pressure or the like).

In one example, the inflow source 312 includes the compressible fluid at a first pressure provided to the cylinder 304. The static liquid piston assembly 300 operates on the compressible fluid to accordingly compress it and then deliver the compressed fluid to the outflow source 314 at a second higher pressure. In another example, the inflow source 312 includes the compressible fluid at a first (relatively) high pressure. The pressurized compressible fluid is delivered to the static liquid piston assembly 300 and accordingly moves the cylinder 304 relative to the piston 302 (away from the piston face 326) in the manner of an expander or engine. The expanded compressible fluid (with the cylinder 304 at an elevated position) is then delivered to the outflow source 314 at a second (relatively) lower pressure, for instance.

As further shown in FIG. 3, a heat exchanger 320 is in one example in communication with the static liquid piston assembly 300. The heat exchanger 320 includes a piston fluid inflow 322 and a piston fluid outflow 324. As shown in FIG. 3, each of the piston fluid inflow and the piston fluid outflow 322, 324 include a corresponding piston fluid inflow port 338 and piston fluid outflow port 340. As described herein, the piston fluid inflow port 338 optionally includes one or more spray ports 344. The heat exchanger 320 extracts or adds heat to the liquid piston fluid 324 depending on the operation of the static liquid piston assembly 300 (e.g., as a compressor or expander). As shown in FIG. 3, each of the piston fluid inflow port 338 and the piston fluid outflow port 340 are provided in communication with the liquid piston fluid 324. That is to say, the ports 338, 340 are at recessed positions relative to the inflow and outflow ports 334, 336 for the compressible fluid. As will be described herein, by conducting heat transfer through the liquid piston fluid 324, a compressible fluid, whether expanded or compressed by the static liquid piston assembly 300, is isothermally acted upon to thereby increase the efficiency of the static liquid piston assembly 300.

In one example, where the static liquid piston assembly 300 is used as a compressor, the compressible fluid is introduced into the cylinder 304 from the inflow source 312 as previously described herein. The cylinder 304 is then operated, for instance, by a drive mechanism connected with the cylinder 308 to accordingly move the cylinder 304 toward the piston 302 (e.g., contraction). The static liquid piston 328, in combination with the moving cylinder 304, compresses the compressible fluid therein. Compression of the compressible fluid generates heat and additional work is required (e.g., from the input device 104) to compress the fluid to the specified value (a specified pressure). The heat exchanger 320 moves the liquid piston fluid 324 in a cyclical fashion from the heat exchanger 320 to the cylinder 304 and the static liquid piston 328. The liquid piston fluid 324 contacts the compressible fluid and provides a heat transfer medium configured to remove heat from the compressed fluid and maintain the compressed fluid at near isothermal conditions (e.g., with no or minimal temperature change in the compressible fluid). Accordingly, energy otherwise spent to offset heat generated during compression is saved by extracting heat from the liquid piston fluid 324 with the heat exchanger. Accordingly, the static liquid piston assembly 300, when used as a compressor, is thereby able to efficiently isothermally compress the fluid (e.g., with minimal or not change in temperature between uncompressed and compressed states) with less work than a system that fails to use the liquid piston fluid as a heat transfer medium.

In contrast, the heat exchanger 320 operates in an inverted configuration with the static liquid piston assembly 300 operated as an expander. In an expander example, the inflow source 312 provides the compressible fluid in a pressurized state to the cylinder 304. The cylinder 304 at a contracted position (relative to the view in FIG. 3) expands because of the pressurized compressible fluid with the cylinder 304 moving away from the piston face 326 and the static liquid piston 328. In one example, the expansion of the compressible fluid decreases its temperature and siphons energy otherwise converted into mechanical output (e.g., movement of the cylinder 304 and corresponding movement of an output device, such as the device 105). Accordingly, heat transfer from the compressible fluid (to the static liquid piston assembly 300, the liquid piston fluid 324 or the like) decreases the efficiency of the static liquid piston assembly 300 operated as an expander.

In one example, the heat exchanger 320 (including a pump associated with the heat exchanger) cycles the liquid piston fluid 324 into and out of the cylinder 304. During expansion the compressible fluid cools and the heat exchanger 320 provides a flow of the (heated) liquid piston fluid 324 to offset the cooling. The heated liquid piston fluid transfers heat to the compressible fluid to offset the expansion based cooling. The compressible fluid thereby expands in a substantially isothermal manner (e.g., with minimal or no change in temperature). Accordingly, the expansion of the compressible fluid is efficiently converted into mechanical output, for instance, movement of the cylinder 304 and the cylinder rod 308. Referring again to FIG. 3, other features that facilitate heat exchange are optionally provided with the static liquid piston assembly 300. As shown in FIG. 3, in one example, a porous media 332 is provided in at least a portion of the cylinder 304. The porous media 332 provides enhanced surface area configured to receive the compressible fluid therein. The relatively large surface area in contact with the compressible fluid provides enhanced heat transfer to the compressible fluid as well as the liquid piston fluid 324. The porous media 332, in one example, includes, but is not limited to, one or more of tubes, posts, fins, interlaced tubes, interlaced posts, interlaced fins, tilted interrupted plates, profiled cylinder cavity walls, metallic foam or wire mesh within the cylinder 304. The increased surface area provided by these features allows the porous media 332 to serve as a heat transfer intermediary to facilitate the enhanced heat transfer from the compressible fluid to the liquid piston fluid 324 (or the converse with expansion) for eventual heat transfer by way of the heat exchanger 320.

The porous media 332 provides an intermediate heat transfer medium between the compressible fluid and the liquid piston fluid 324. In one example, the compressible fluid heats the porous media 332 during compression. The (heated) porous media 332 is infiltrated by the liquid piston fluid 324 as part of the compression stroke. The porous media 332 within the cylinder 304 meets and passes through the static liquid piston interface 330. The liquid piston fluid 324 infiltrates the passages or other features of the porous media 332 and engages the porous media 332 across its enhanced surface area according to one or more of the features previously described herein. The liquid piston fluid 324 accordingly extracts heat from the porous media 332. The extracted heat is transferred from the liquid piston fluid 324 at the heat exchanger 320.

The heat exchanger 320 including, for instance, a pump and one or more heat exchange features extracts heat from the liquid piston fluid 324 and returns cooled liquid piston fluid 324 to the cylinder 304 through the piston fluid inflow 322.

In another example, where the static liquid piston assembly 300 is operated as an expander the compressible fluid is introduced to the cylinder 304 with the cylinder 304 in a descended configuration. As the cylinder 304 rises with expansion of the compressible fluid the compressible fluid begins to cool. In such an example, the porous media 332 is infiltrated by the liquid piston fluid 324 (submerged within the fluid 324) while the cylinder 304 is at least partially contracted. The heated liquid piston fluid 324 heats the porous media 332. As the cylinder expands the heated porous media 332 transfer heat to the expanding compressible fluid to maintain the compressible fluid at isothermal conditions (e.g., with minimal or no temperature change).

In still another example, the static liquid piston assembly 300 includes one or more spray ports 344. Optionally, the spray ports 344 are provided in place of the porous media 332. In another example, the porous media 332 and the spray ports 344 are provided in combination to the static liquid piston assembly 300. The spray ports 344 are, in one example, in communication with the heat exchanger 320. For instance, the piston fluid outflow 324, in one example, also or alternatively communicates with the spray ports 344 to provide a flow of atomized liquid piston fluid 324 into the cylinder 304. The enhanced surface area provided by the atomized liquid piston fluid 324 ensures enhanced heat transfer between the compressible fluid and the liquid piston fluid 324. The atomized drops of the liquid piston fluid absorb heat and settle into the static liquid piston 328 and are thereafter cycled out of the cylinder 304 to the heat exchanger 320.

FIGS. 4A and 4B show one example of a static liquid piston system 400. In the example shown in FIGS. 4A and 4B, the static liquid piston system 401 is operated as a compressor. The static liquid piston system 401, in the example, includes a static liquid piston assembly 300 previously shown and described, for instance, in FIG. 3. One or more features of the assembly shown in FIG. 3, such as the heat exchanger 320, inflow and outflow sources 312, 314 are omitted for clarity. Referring first to FIG. 4A, the static liquid piston assembly 300 is shown in a filled configuration, for instance, with a compressible fluid 402 within the cylinder cavity 405. The cylinder cavity 405 includes a porous media 332 within a portion of the cylinder cavity 405. As previously described herein, the porous media 332, in one example, facilitates heat transfer, for instance, from the compressible fluid 402 to the liquid piston fluid 324 for eventual extraction from the static liquid piston assembly 300, for instance by the heat exchanger 320 shown in FIG. 3. The removal of heat by way of one or more of the liquid piston fluid 324, the porous media 332 (and optionally the spray ports 344 shown in FIG. 3) facilitates the operation of the static liquid piston system 401 in an isothermal manner.

As further shown in FIG. 4A, the static liquid piston system 401 includes one example of an input system, for instance, an input device 104 such as an input shaft coupled with an input 106 including, but not limited to a drive shaft. The input device 104 optionally includes a cam 400 to reciprocate the cylinder rod 308 extending through the static liquid piston assembly 300 and coupled with the cylinder head 306. Other examples of reciprocating drive mechanisms are provided herein and include connecting rods and corresponding joints such as the shaft joint 122 and cylinder joint 124 shown in FIG. 1A. In other examples, the input device 104 includes one or more other features, for instance, a crank, reciprocal drive feature or the like configured to move the cylinder 304 in a reciprocating manner relative to the piston 302.

As further shown in FIG. 4A, the liquid piston fluid 324 is provided along the piston face 326 of the piston 302. As previously described herein, liquid piston fluid 324 is statically held within the static liquid piston assembly 300 while the cylinder 304 moves relative to the static liquid piston 328 (including the fluid 324 as well as the piston face 326).

Transitioning from the filled configuration shown in FIG. 4A to the compressed configuration shown in FIG. 4B (a contracted configuration relative to that shown in FIG. 4A), the cylinder 304 is shown in a lower position relative to the position shown in FIG. 4A. In this example, the connector rod 308 is pulled downwardly relative to the piston 302 to accordingly compress the compressible fluid 402 within the cylinder cavity 405. As shown in FIG. 4B, the liquid piston fluid 324 has infiltrated at least a portion of the porous media 332. The remainder of the porous media 332 is infiltrated by the compressible fluid 402 and is compressed.

In one example, one or more outflow features are opened with the static liquid piston assembly 300 in the compressed configuration. For instance, a pressure operated valve (e.g., a pressure operated unidirectional valve 342) is opened to allow the compressed fluid to escape the cylinder cavity 405 for delivery to the outflow source 314 shown in FIG. 3. An outflow port 336 (as well as an inflow port 334) are shown just above the liquid piston interface 330 and thereby remain in communication with the compressible fluid whether the cylinder 304 is in the expanded or contracted configurations. In one example, the porous media 332, including one or more of cylinders, fins, meshes, one or more of tubes, posts, fins, interlaced tubes, interlaced posts, interlaced fins, tilted interrupted plates, profiled cylinder cavity walls, metallic foam or wire mesh or a variety of other geometries within the cylinder cavity 405, includes one or more passages, recesses or the like therein to facilitate the passage of the inflow and outflow ports 334, 336 into the porous media 332 as the cylinder 304 with the media moves relative to the piston and the ports. In another example, the inflow and outflow ports 334, 336 are instead coupled with the cylinder 304, for instance, by way of one or more flexible couplings extending to the inflow and outflow sources 312, 314, respectively.

As shown in FIG. 4B, the liquid piston fluid 324 of the static liquid piston 300 is received within at least a portion of the porous media 332. As previously described herein, the porous media 332 provides an optional heat transfer intermediate configured to transfer heat, for instance, from the compressible fluid 402 developed during compression of the compressible fluid by the static liquid piston system 401 to the liquid piston fluid 324. The porous media 332 includes one or more features such as fins, pins, metal foam, wire matrixes, fluting (as previously described herein) that increase the surface area of the porous media 332 and facilitate heat transfer from the compressible fluid 402 to the porous media 332 and from the porous media 332 to the liquid piston fluid 324. The heat transferred from the compressible fluid 402 from its expanded to compressed configurations (corresponding to FIGS. 4A and 4B, respectively) is extracted from the static liquid piston assembly 300, for instance, by the heat exchanger 320 in communication with the liquid piston fluid 324. The heat transfer from the compressible fluid 402 to the liquid piston fluid 324 minimizes the increase in temperature of the compressed fluid 402 and accordingly ensures mechanical work conducted by the static liquid piston assembly 300 and the input 106 efficiently compresses (e.g., isothermally) the compressible fluid 402. The static liquid piston system 401 with the heat transfer mechanisms described herein is thereby able to operate in an isothermal manner (e.g., including isothermal or near isothermal) to increase the efficiency of the static liquid piston assembly 300 relative to other compressor systems.

FIGS. 5A and 5B show another example of a static liquid piston system 501. In this example, the system 501 is operated in the manner of an expander, such as an engine. That is to say, compressible fluid within the cylinder cavity 405 is expanded to accordingly move one or more mechanical features such as the cylinder rod 308 shown in FIGS. 5A and 5B and thereby output work from the static liquid piston system 501, for instance, to the output 128. The system 501 includes components similar to at least the system 401 (operated as a compressor) previously described herein.

Referring first to FIG. 5A, the cylinder 304 is shown in a contracted position relative to the piston 302. The compressible fluid 402 is provided above the liquid piston interface 330. In this configuration, the compressible fluid 402 is compressed and provided through one or more inflow ports such as the inflow port 334 shown in FIG. 3. The compressible fluid expands the cylinder cavity 405 and drives the cylinder 304 in an upward fashion as shown with the arrow in FIG. 5A and shown in an expanded configuration in FIG. 5B. As further shown in FIG. 5A and similarly previously shown in FIG. 4B, the liquid piston fluid 324 at least partially infiltrates the porous media 332 of the static liquid piston assembly 300. As previously described herein, the infiltration of the liquid piston fluid 324 into the porous media 332 efficiently transfers heat from the compressible fluid 402 and into the liquid piston fluid 324 because of the relatively large surface area of the porous media. In the expander example shown in FIG. 5A, the porous media 332 in combination with the liquid piston fluid 324 transfers heat to the compressible fluid 402. The liquid piston fluid 324 within the porous media 332 is, in one example, heated by the heat exchanger 320 shown in FIG. 3. The heated liquid piston fluid 324 is provided through the piston fluid infusion port 338 (see FIG. 3) and heats the porous media 332 (prior to the expansion of the cylinder relative to the static liquid piston 328). The heat transferred to the porous media 332 is transferred from the media to the compressible fluid 402 that has infiltrated the porous media 332.

Referring now to FIG. 5B, the static liquid piston assembly 300 is shown in an expanded configuration with the expanded compressible fluid 402 having raised the cylinder 304 relative to the piston 302. Accordingly, the cylinder rod 308 is similarly raised relative to the piston 302 and transmits reciprocating motion to the cam 400 (alternatively a crank or the like) provided with the output device 105. The output device 105, in one example, rotates one or more outputs 128 coupled with the output device 105.

Referring again to FIG. 5B, the compressible fluid 402 is shown in both of the porous media 332 as well as the remainder of the cylinder cavity 405. As the compressible fluid 402 expands under normal adiabatic conditions the fluid cools. However, in the arrangement shown in FIG. 5B, with the heat transfer to the porous media 332 along with the heated liquid piston fluid 324 of the static liquid piston 328, the compressible fluid 402 is isothermally heated during expansion and maintains its temperature (e.g., including limited or no variation in temperature). That is to say, a temperature change in the compressible fluid 402 is minimized to accordingly increase the output and corresponding efficiency of the static liquid piston system 501.

As previously described herein, in one example one or more spray ports 344 are provided in the static liquid piston assembly 300. In each of the examples shown herein, including the expander system 502 shown in FIGS. 5A and 5B and the compressor system 402 shown in FIGS. 4A and 4B, the spray ports 344 are optionally in communication with the heat exchanger 320 to provide one or more of heated or cooled liquid piston fluid 324 in sprayed drops (e.g., atomized) to the cylinder cavity 405. The atomized liquid piston fluid is, in one example, heats the compressible fluid in the example of the expander shown in FIGS. 5A and 5B and, in another example, the atomized liquid piston fluid from the spray ports 344 cools the compressible fluid during compression, for instance, by the static liquid piston system 401 shown in FIGS. 4A, 4B.

In yet another example, the fluid interface between the static liquid piston 328 and the compressible fluid 402 is used by itself to provide heat transfer between the compressible fluid 402 and the liquid piston fluid 324. Stated another way, in one example the heat transfer intermediates or features provided herein, including the porous media 332 and the one or more spray ports 344, are absent from the static liquid piston assemblies described herein. In another example, a combination of one or more of the spray ports 344, the porous media 332 and the heat exchanger 320 and its associated components are used in combination or alone to provide heat transfer between the compressible fluid 402 and the liquid piston fluid 324.

FIG. 6 shows another example of a liquid piston assembly 600. As shown, the liquid piston assembly 600 includes a cylinder 604 and a piston 602. In this example, the piston 602 is moveable relative to the cylinder 604. That is to say, the cylinder 604 is static and the piston 602 including the liquid piston fluid 606 along the piston 602 moves with the piston 602 as it reciprocates relative to the static cylinder 604. In at least some other regards, the liquid piston assembly 600 includes features previously described herein. For instance, in the example, the liquid piston assembly 600 includes a porous media 332 provided within the static cylinder 604. The porous media 332, as described herein provides a heat transfer interface for use with the liquid piston fluid 606. For instance, the porous media 332 includes one or more of a reticulated foam such as a metal foam, wire mesh, pins, posts, tubes, fins or the like within the static cylinder 604 to provide increased surface area for contact with the liquid piston fluid 606, for instance, when the moveable piston 602 is moved upwardly relative to the static cylinder 604 to move the liquid piston fluid 606 into the interstitial spaces (recesses, passages, openings or the like) of the porous media 332.

As shown in FIG. 6, the liquid piston fluid 606 includes a disturbed liquid piston interface 608. In contrast to the liquid piston interface as described herein, the disturbed liquid piston interface 608 is, in one example, disturbed by one or more of the movement of the moveable piston 602, shearing forces along the static cylinder 604 relative to the moveable piston 602 and the like. For example, when the moveable piston 602 is operated at a frequency, for instance, greater than two hertz (e.g., greater than 2.2 hertz corresponding to an acceleration of gravity of 9.81 meters per second squared) the liquid piston fluid 606 splashes away from the moveable piston 602, for instance, along the walls of the static cylinder 604 and, in some examples, along the porous media 632 or the upper surface of the static cylinder 604 corresponding to the cylinder head. The liquid piston fluid 606 is thereby disturbed and spread throughout the static cylinder 604. The mixing of the liquid piston fluid 606 with the compressible fluid within static cylinder 604 mixes the compressible fluid into the liquid piston fluid 606. As shown in FIG. 6, mixed compressible fluid bubbles 612 are shown mixed into the liquid piston fluid 606.

Additionally, the liquid piston fluid 606 is sheared and correspondingly spread along a portion of the static cylinder 604 walls with relative movement between the piston 602 and the cylinder 604. In one example, a combination of the reciprocation of the moveable piston 602, for instance at higher accelerations (and decelerations) such as one (1) gravity or greater, and the viscoelastic properties of the liquid piston fluid 606 and shearing of the same generate the disturbed liquid piston interface 608. The disturbance of the liquid piston fluid 606 mixes the liquid piston fluid 606 with the compressible fluid as described herein. The mixing of the compressible fluid into the liquid piston fluid 606 accordingly consumes volume within the static cylinder 604 otherwise used by the compressible fluid, for instance, for expansion or compression. Accordingly, the available volume for expansion or compression is smaller relative to a liquid piston assembly having an relatively undisturbed liquid piston interface (as described in other examples herein). Instead, with the smaller volume shown in FIG. 6, the compressible fluid is expanded or compressed to a smaller extent relative to the previously described assemblies. Accordingly, the efficiency including one or more of the compression ratio, expansion ratio or the like of the liquid piston assembly 600 is decreased relative to that of the other liquid piston assemblies described herein including static liquid pistons.

As further shown in FIG. 6, in one example, interstitial liquid piston fluid 615 is retained in the porous media 332 while the liquid piston fluid 606 is otherwise withdrawn from the porous media 332 (e.g., in an expanded configuration as shown in FIG. 6). For instance, as the moveable piston 602 descends relative to the porous media 332, some of the liquid piston fluid 606, in some examples is retained in one or more interstitial spaces within the porous media 332. In some examples, the retention of the interstitial liquid piston fluid 615 also traps compressible fluid therein. The trapped compressible fluid 614 is shown as bubbles provided adjacent at least some of the interstitial liquid piston fluid 615. In a similar manner to the mixed compressible fluid bubbles 612, the trapped compressible fluid 614 as well as the interstitial liquid piston fluid 615 consume the volume of the static cylinder 604 and accordingly decrease the compression or expansion ratios of the liquid piston assembly 600. Accordingly, the efficiency of the liquid piston assembly 600 is decreased. Further, the interstitial liquid piston fluid 615 blocks or prevents the infiltration of the compressible fluid into the porous media 332, for instance, as part of compression or expansion. The decrease of infiltration of the compressible fluid into the porous media 332 further decreases the volume of the static cylinder 604 and correspondingly further decreases one or more of the compression or expansion ratios of the liquid piston assembly 600.

Although the interstitial liquid piston fluid 615 and the trapped compressible fluid 614 shown in FIG. 6 are provided in an example liquid piston assembly 600 including a moveable piston 602 in contrast to the static pistons such as the piston 110 shown in FIG. 1A, trapping and retention of liquid piston fluid within the porous media 332 occurs in some examples with the static liquid piston assemblies described herein previously. For instance, in FIG. 3, the porous media 332, in some examples, may retain liquid piston fluid in the manner of the interstitial liquid piston fluid 615 shown in FIG. 6. In one example, the porous media 332 is provided with passages (e.g., interstices) large enough to freely pass the liquid piston fluid 606 therethrough. Accordingly, with movement of the cylinder such as the cylinder 304 in FIG. 3 and corresponding movement of the liquid piston fluid 324 relative to the porous media 332 the liquid piston fluid readily escapes the porous media 332 and the volume of the cylinder 304 is maintained to thereby enhance the effectiveness of the static liquid piston assembly 300 whether used as a compressor, expander or the like.

In another example, the porous media 332 includes one or more phobic coatings provided along the surfaces of the porous media 332. The phobic coatings repel (e.g., shed) the liquid piston fluid 606 and accordingly ensure interstitial liquid piston fluid 615 as shown in FIG. 6 is minimized. For instance, in one example where the liquid piston fluid 606 includes water a hydrophobic coating is provided to the porous media 332 to facilitate the escape of the liquid piston fluid 606 from the porous media 332. In a similar manner where the liquid piston fluid 606 comprises an oil the porous media 332 includes an oleophobic coating configured to maximize the escape of the liquid piston fluid 606 from the porous media 332. Optionally, the phobic coating is provided along the walls of the cylinder to minimize shearing and spreading of the liquid piston fluid along the cylinder walls (e.g., including the side walls, cylinder head or the like).

FIG. 7 shows another example of a static liquid piston assembly 700. In the example shown in FIG. 7, the assembly 700 includes a ferrofluid anchor system 718. The ferrofluid anchor system 718 includes a ferrofluid 710 as the liquid piston fluid used with the piston 702. The ferrofluid anchor system 718 including the ferrofluid 710 minimizes the movement of the ferrofluid 710 for instance by way of shearing forces provided between the cylinder 704 and the ferrofluid 710 and minimizes splashing, for instance, where the cylinder 704 is reciprocated at one or more of a relatively high frequency or high acceleration, for instance, one or more of frequencies greater than 1 Hz or accelerations (and decelerations) around one (1) gravity or more. Further, the ferrofluid anchor system 718 readily withdraws the ferrofluid 710 from a media, such as the porous media 332 optionally provided in the cylinder 704. Accordingly, interstitial liquid piston fluid within the porous media 332 as previously described and shown in FIG. 6 is instead avoided or minimized with the ferrofluid anchor system 718 shown with the assembly 700 of FIG. 7.

Referring again to FIG. 7, the static liquid piston assembly 700 includes a variety of features similar in at least some regards to the previously described liquid piston assemblies provided herein. For instance, the assembly 700 includes a moveable cylinder 704 that reciprocates relative to a piston 702. The cylinder 704 includes a cylinder cavity 706 sized and shaped to receive the compressible fluid 708 therein. The static liquid piston assembly 700 is operated in one or more examples as one or more of a compressor or expander (e.g., an engine). As further shown in FIG. 7, the ferrofluid 710 is provided as the liquid piston fluid for the static liquid piston 714. The static liquid piston 714 thereby includes the piston 702 and the ferrofluid 710 provided along the piston face 703. In many regards, the ferrofluid 710 behaves in a similar manner with regard to operation of the static liquid piston assembly 700. For instance, the ferrofluid 710 remains in a substantially static state along the piston 702 because the piston 702 is static relative to the moveable cylinder 704. Instead, the cylinder 704 moves with respect to the piston 702 including the static liquid piston 714 to thereby maintain the ferrofluid 710 as the liquid piston in place. Accordingly, the liquid piston interface 716 maintains a substantially undisturbed configuration and the assembly 700 is operable at frequencies greater than operation frequencies with moving liquid pistons.

As further shown in FIG. 7, the fluid anchor system 718 includes the ferrofluid 710 and one or more retention magnets 712, for instance provided within the piston 702. In one example, the anchor system 718 includes at least one retention magnet 712 provided in close proximity to or along the piston face 703. The retention magnet 712 interacts with the ferrofluid 710 and biases the ferrofluid 710 toward the piston face 703. In one example, the one or more retention magnet 712 include but are not limited to a permanent magnet such as a neodymium magnet, an electromagnet or the like. Magnetic forces provided by the retention magnet 712 to the ferrofluid 710 counteract forces on the ferrofluid 710 generated by shearing of the fluid along the walls of the cylinder 704.

Magnetic forces provided by the retention magnet 712 further bias the ferrofluid 710 into the configuration shown in FIG. 7 (e.g., substantially undisturbed) with regard to the porous media 332 as well. Accordingly, interstitial retention of at least a portion of the ferrofluid 710 within the porous media 332 is counteracted by the magnetic bias provided by the retention magnet 712 to the ferrofluid 710. Further, the retention magnet 712 stabilizes the liquid piston interface 716. Accordingly, in one example, the static liquid piston assembly 700 including the ferrofluid anchor system 718 described herein is configured to operate at higher frequencies relative to other liquid piston systems because of the magnetic bias. Optionally, the ferrofluid anchor system 718 is, in one example, used in combination with one or more of the other features configured to retain the liquid piston fluid along the piston face 703. In one example, one or more phobic coatings are provided to the cylinder 704 such as the cylinder walls, the porous media 332 or the like to facilitate shedding of the ferrofluid and retention of the ferrofluid 710 along the piston face 703. Accordingly, with one or more of these features including the ferrofluid anchor system 718, phobic coatings provided to one or more of the cylinder wall, the porous media 332 or the like as well as the reciprocation of the cylinder 704 as opposed to the piston 702, a substantially undisturbed liquid piston interface 716 is provided with the static liquid piston assembly 700. The ferrofluid anchor system 718 is readily included in the other liquid piston assemblies described herein.

In one example, the ferrofluid 710 includes one or more of a liquid substrate with ferrous particles suspended within the fluid. Optionally, a surfactant is included within the ferrofluid to minimize the aggregation of the ferrous particles. In another example, the ferrofluid 710 includes a colloid consisting of subdomain magnetic particles that are optionally coated with a surfactant as previously described herein and suspended within a carrier liquid such as an oil. The surfactant is, in one example, matched to the carrier fluid such that it overcomes attractive van der Waals and magnetic forces between particles and thereby prevents agglomeration. When the ferrofluid 710 is exposed to a magnetic field, for instance from the one or more retention magnets 712, the ferrofluid 710 experiences a magnetic force (e.g., a downward magnetic force) that biases the ferrofluid 710 toward the piston face 703.

Optionally, the one or more retention magnets 712 are provided along the piston face 703, for instance, at the edges of the piston face 703. Accordingly, the ferrofluid 710 is biased toward the interface between the cylinder 704 and the piston 702. The ferrofluid 710 acts as a lubricant between the cylinder 704 and the piston 702 and is biased toward that location by the retention magnet 712. Accordingly, a seal is reliably maintained between the bearing surfaces of the cylinder 704 and the piston 702 throughout operation of the static liquid piston assembly 700.

Further, the static liquid piston assembly 700 including the ferrofluid anchor system 718, in one example, facilitates the use of a porous media 332 having smaller interstitial spaces (e.g., gaps, grooves, passage or the like). For instance, the retention magnet 712 readily draws the ferrofluid 710 out of relatively smaller passages within the porous media 332. That is to say, the magnetic bias provided by the retention magnet 712 draws the ferrofluid 710 out of the porous media 332 having smaller passages, spaces, recesses or the like compared to other media. The porous media includes a larger number of these smaller passages, spaces or the like in a tightly packed configuration and accordingly includes an even larger surface area relative to other media. The enhanced surface area increases heat transfer efficiency of the porous media 332 when used with the ferrofluid anchor system 718. The static liquid piston assembly 700 is thereby able to operate as a compressor or an expander as described herein in a more efficient fashion with the ferrofluid anchor system 718.

FIG. 8 shows one example of a method 800 of using a static liquid piston system, as described herein. In describing the method 800, reference is made to one or more components, features, functions, steps or the like described herein. Where convenient reference is made to the components, features, functions, steps and the like with reference numerals. Reference numerals provided are exemplary and are not exclusive. For instance, the features, components, functions, steps or the like described in the method 800 include, but are not limited to, the corresponding numbered elements, other corresponding features described herein (both numbered and unnumbered) as well as their equivalents.

At 802, a compressible fluid is introduced to a cylinder cavity 202 of a reciprocating (e.g., movable) cylinder 108 in an expanded position relative to a piston 110. One example of a cylinder and piston is shown in FIG. 2. The compressible fluid is introduced at a first temperature. At 804, the compressible fluid is isothermally compressed within the cylinder cavity 202. Isothermal compression with the static liquid piston system includes (at 806) moving the reciprocating cylinder 108 (from an expanded position) toward a contracted position relative to a static liquid piston 328 to compress the compressible fluid 402. One example of compression and the transition from the expanded position to the contracted position is shown in FIGS. 4A, B. As previously described herein, in one example compression of the compressible fluid increases the fluid temperature (e.g., adds heat to the compressible fluid and the surrounding system). At 808, the method 800 includes extracting heat from the compressible fluid (and the surrounding system) generated with compression. Examples of heat transfer (including heat extraction) are provided herein including, but not limited to heat transfer from the compressible fluid to the liquid piston fluid of the static liquid piston, intermediate heat transfer from the compressible fluid to one or more of a porous media or a spray of the liquid piston fluid or the like.

At 810, the compressed compressible fluid is evacuated from the cylinder cavity at a second temperature near the first temperature. The heat transfer between the compressible fluid and the liquid piston fluid minimizes heat (temperature) fluctuations in the static liquid piston system including, for example, the static liquid piston assembly 300 shown in FIG. 3. The compressible fluid is thereby compressed in an isothermal manner (e.g., including near isothermal manner having a change in temperature during compression of one or more of 0, 1, 5, 10, 15, 20, 25 or 30 degrees Celsius or the like) and energy otherwise wasted in the generation of heat is instead efficiently used for compression of the fluid. In other examples, the static liquid piston systems described herein show examples of heat transfer to the compressible fluid, for instance where the systems are used as expanders (e.g., engines) to isothermally expand the compressible fluid.

Several options for the method 800 follow. In one example, the static liquid piston 328 includes liquid piston fluid 324. Extracting heat from the compressible fluid includes transferring heat from the compressible fluid to material of the reciprocating cylinder (including the cylinder material, a porous media or the like). Heat is transferred to the liquid piston fluid from the material of the reciprocating cylinder, such as a porous (heat transfer) media, the material of the cylinder such as the cylinder wall or the like. In another example, the method 800 includes cycling the heated liquid piston fluid 324 through a heat exchanger, such as the heat exchanger 320 shown in FIG. 3. Heat is extracted from the liquid piston fluid 324 at the heat exchanger. In an example, including porous media (e.g., porous heat transfer media) 332 heat is transferred from the compressible fluid to the porous media in intimate contact with the compressible fluid during compression, for instance with the compressible fluid infiltrating the porous media. Transferring heat to the liquid piston fluid includes transferring heat from the porous media 332 to the liquid piston fluid 324 while the fluid 324 is in intimate contact with the porous heat transfer media at least in the contracted position. As described herein, in one example moving the reciprocating cylinder 304 toward the contracted position relative to the static liquid piston 328 includes infiltrating the porous heat transfer media 332 with the liquid piston fluid 324 (see FIG. 4B).

In another example, extracting heat from the compressible fluid includes spraying a heat sink fluid into the reciprocating cylinder 304. Optionally, the heat sink fluid includes the liquid piston fluid 324. In another example, the heat sink fluid includes an immiscible fluid that does not mix with the liquid piston fluid 324 (e.g., one is an oil, the other water in one example) and is readily cycled out of the static liquid piston assembly 300. The method 800 includes extracting heat from the compressible fluid with the sprayed heat sink fluid. The heated sprayed heat sink fluid mixes with the liquid piston fluid according to settling of the heated sprayed heat sink fluid toward the static liquid piston 328. In other examples, the method includes operation of the system as an expander (e.g., engine) that generates power by expansion of a compressed compressible fluid with movement of the cylinder 304 relative to the static liquid piston 328. The system is operated substantially in reverse and instead of transferring heat from the compressible fluid to the liquid piston fluid the expander system transfers heat to the compressible fluid to isothermally expand the compressible fluid.

In still another example, isothermally compressing (or expanding) the compressible fluid includes reciprocating the reciprocating cylinder relative to the static liquid piston at an operating frequency that decelerates (and conversely accelerates) the reciprocating cylinder at a deceleration and acceleration) greater than one gravity.

As described herein, the static liquid piston includes a liquid piston fluid 324 along a piston face 326. The method 800 includes retaining the liquid piston fluid 324 along the piston face 326. In one example, the liquid piston fluid includes a liquid piston ferrofluid (e.g., ferrofluid 710 shown in FIG. 7) as part of a ferrofluid anchor system 718. Retaining the liquid piston fluid along the piston face 703 includes biasing the liquid piston ferrofluid 710 toward the piston face with a retention magnet 712 another component of the ferrofluid anchor system 718. In another example, the reciprocating cylinder includes a porous heat transfer media 332. In such an example, retaining the liquid piston fluid (e.g., the ferrofluid 710) along the piston face 703 includes extracting the liquid piston ferrofluid 710 from interstitial locations within the porous heat transfer media 332 according to biasing of the liquid piston ferrofluid 710 toward the piston face 703 at least during retraction of the reciprocating cylinder from the contracted position. In another example, retaining the liquid piston fluid 710 along the piston face 703 includes biasing the liquid piston ferrofluid 710 toward a moving interface between the reciprocating cylinder and the piston face. As described herein, the retention magnet 712 biases the liquid piston fluid 710 toward the piston face 703. In one example, the biased liquid piston fluid 710 spreads across the piston face 704 and readily maintains a seal between the cylinder 704 (including the cylinder wall) and the piston face 703. Optionally, the retention magnet (or magnets) 712 is positioned around the perimeter of the piston 702 (e.g., near the edges of the piston face 703) to thereby bias and reliably position the ferrofluid 710 at the cylinder piston interface. The ferrofluid 710 is in one example used as a lubricant and sealant for the static liquid piston assembly 700.

Various Notes & Examples

Example 1 can include subject matter such as can include a liquid piston compressor system comprising: a drive mechanism; a compressor assembly coupled with the drive mechanism, the compressor assembly includes: a reciprocating cylinder coupled with the drive mechanism, the reciprocating cylinder includes a cylinder cavity and a cylinder head, and a static liquid piston received in the cylinder cavity, the static liquid piston includes a piston face configured to carry liquid piston fluid; and wherein the reciprocating cylinder is configured to move relative to the static liquid piston between contracted and expanded positions to compress a compressible fluid: in the expanded position the cylinder head is withdrawn from liquid piston fluid and the cylinder cavity is filled with the compressible fluid, and in the contracted position the cylinder head is near the liquid piston fluid and the compressible fluid is compressed.

Example 2 can include, or can optionally be combined with the subject matter of Example 1, to optionally include liquid piston fluid carried on the piston face.

Example 3 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1 or 2 to optionally include wherein the liquid piston fluid includes a liquid piston ferrofluid, and the static liquid piston includes a retention magnet configured retain the liquid piston ferrofluid along the piston face.

Example 4 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1-3 to optionally include wherein liquid piston fluid is a heat sink or heat source.

Example 5 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1-4 to optionally include wherein the compressor assembly includes a heat exchanger in communication with the liquid piston fluid, and the heat exchanger is configured to extract heat from the liquid piston fluid heated by the compressed compressible fluid.

Example 6 can include, or can optionally be combined with the subject matter of Examples 1-5 to optionally include a compressible fluid, and the compressible fluid is isothermal between the expanded and contracted positions according to the liquid piston fluid heat sink and the operation of the heat exchanger.

Example 7 can include, or can optionally be combined with the subject matter of Examples 1-6 to optionally include wherein the reciprocating cylinder includes a porous heat transfer media within the cylinder cavity.

Example 8 can include, or can optionally be combined with the subject matter of Examples 1-7 to optionally include wherein the porous heat transfer media consists of one or more of tubes, posts, fins, interlaced tubes, interlaced posts, interlaced fins, tilted interrupted plates, profiled cylinder cavity walls, metallic foam or wire mesh.

Example 9 can include, or can optionally be combined with the subject matter of Examples 1-8 to optionally include wherein the porous heat transfer media includes a phobic coating.

Example 10 can include, or can optionally be combined with the subject matter of Examples 1-9 to optionally include wherein the compressor assembly includes one or more spray ports configured to spray a heat sink fluid into the cylinder cavity.

Example 11 can include, or can optionally be combined with the subject matter of Examples 1-10 to optionally include liquid piston fluid housed on the piston face, and the sprayed heat sink fluid is the same as the liquid piston fluid.

Example 12 can include, or can optionally be combined with the subject matter of Examples 1-11 to optionally include a liquid piston compressor assembly comprising: a reciprocating cylinder including a cylinder cavity and a cylinder head; a static liquid piston received in the cylinder cavity, the static liquid piston includes: a piston face, a liquid piston ferrofluid along the piston face, and a retention magnet; and wherein the reciprocating cylinder is configured to move relative to the static liquid piston between contracted and expanded positions: in the expanded position the cylinder head is withdrawn from the liquid piston ferrofluid, in the contracted position the cylinder head is near the liquid piston ferrofluid, and the retention magnet is configured to retain the liquid piston ferrofluid along the piston face in each of the expanded and contracted positions and during movement therebetween.

Example 13 can include, or can optionally be combined with the subject matter of Examples 1-12 to optionally include wherein the liquid piston ferrofluid includes a liquid base and a plurality of ferrous particles suspended in the liquid base.

Example 14 can include, or can optionally be combined with the subject matter of Examples 1-13 to optionally include wherein the liquid piston ferrofluid includes a surfactant.

Example 15 can include, or can optionally be combined with the subject matter of Examples 1-14 to optionally include wherein the reciprocating cylinder includes a porous heat transfer media within the cylinder cavity.

Example 16 can include, or can optionally be combined with the subject matter of Examples 1-15 to optionally include wherein the retention magnet is configured to extract the liquid piston ferrofluid from interstitial locations of the porous heat transfer media with movement of the reciprocating cylinder between the contracted and expanded positions.

Example 17 can include, or can optionally be combined with the subject matter of Examples 1-16 to optionally include a heat exchanger in communication with the liquid piston ferrofluid, wherein the heat exchanger is configured to extract heat from the liquid piston ferrofluid, the liquid piston ferrofluid heated by compression of a compressible fluid with movement of the reciprocating cylinder between the expanded and contracted positions.

Example 18 can include, or can optionally be combined with the subject matter of Examples 1-17 to optionally include wherein the compressible fluid is isothermal between the expanded and contracted positions according to the liquid piston ferrofluid and the operation of the heat exchanger.

Example 19 can include, or can optionally be combined with the subject matter of Examples 1-18 to optionally include a method of using a liquid piston compressor system comprising: introducing a compressible fluid at a first temperature to a cylinder cavity of a reciprocating cylinder in an expanded position; isothermally compressing the compressible fluid within the cylinder cavity, compressing including: moving the reciprocating cylinder toward a contracted position relative to a static liquid piston to compress the compressible fluid, and extracting heat from the compressible fluid, the heat generated with compression of the compressible fluid; and evacuating the compressed compressible fluid from the cylinder cavity at a second temperature near the first temperature.

Example 20 can include, or can optionally be combined with the subject matter of Examples 1-19 to optionally include wherein the static liquid piston includes liquid piston fluid, and extracting heat from the compressible fluid includes: transferring heat from the compressible fluid to material of the reciprocating cylinder, transferring heat to the liquid piston fluid from the material of the reciprocating cylinder, cycling the heated liquid piston fluid through a heat exchanger, and extracting heat from the liquid piston fluid at the heat exchanger.

Example 21 can include, or can optionally be combined with the subject matter of Examples 1-20 to optionally include wherein the material of the reciprocating cylinder includes a porous heat transfer media, and transferring heat from the compressible fluid to the material of the reciprocating cylinder includes transferring heat to a porous heat transfer media within the reciprocating cylinder in intimate contact with the compressible fluid during isothermal compression, and transferring heat to the liquid piston fluid includes transferring heat from the porous heat transfer media to the liquid piston fluid in intimate contact with the porous heat transfer media at least in the contracted position.

Example 22 can include, or can optionally be combined with the subject matter of Examples 1-21 to optionally include wherein moving the reciprocating cylinder toward the contracted position relative to the static liquid piston includes infiltrating the porous heat transfer media with the liquid piston fluid.

Example 23 can include, or can optionally be combined with the subject matter of Examples 1-22 to optionally include wherein extracting heat from the compressible fluid includes: spraying a heat sink fluid into the reciprocating cylinder, extracting heat from the compressible fluid with the sprayed heat sink fluid, and mixing the heated sprayed heat sink fluid with the liquid piston fluid according to settling of the heated sprayed heat sink fluid.

Example 24 can include, or can optionally be combined with the subject matter of Examples 1-23 to optionally include wherein isothermally compressing the compressible fluid includes reciprocating the reciprocating cylinder relative to the static liquid piston at an operating frequency that decelerates the reciprocating cylinder at a deceleration greater than one gravity.

Example 25 can include, or can optionally be combined with the subject matter of Examples 1-24 to optionally include wherein the static liquid piston includes a liquid piston fluid along a piston face and comprising retaining the liquid piston fluid along the piston face.

Example 26 can include, or can optionally be combined with the subject matter of Examples 1-25 to optionally include wherein the liquid piston fluid includes a liquid piston ferrofluid, and retaining the liquid piston fluid along the piston face includes biasing the liquid piston ferrofluid toward the piston face with a retention magnet.

Example 27 can include, or can optionally be combined with the subject matter of Examples 1-26 to optionally include wherein the reciprocating cylinder includes a porous heat transfer media, and retaining the liquid piston fluid along the piston face includes extracting the liquid piston ferrofluid from interstitial locations within the porous heat transfer media according to biasing of the liquid piston ferrofluid toward the piston face at least during retraction of the reciprocating cylinder from the contracted position.

Example 28 can include, or can optionally be combined with the subject matter of Examples 1-27 to optionally include wherein retaining the liquid piston fluid along the piston face includes biasing the liquid piston ferrofluid toward a moving interface between the reciprocating cylinder and the piston face.

Each of these non-limiting examples can stand on its own, or can be combined in any permutation or combination with any one or more of the other examples.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B.” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third.” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 

What is claimed is:
 1. A liquid piston compressor system comprising: a drive mechanism; a compressor assembly coupled with the drive mechanism, the compressor assembly includes: a reciprocating cylinder coupled with the drive mechanism, the reciprocating cylinder includes a cylinder cavity and a cylinder head, and a static liquid piston received in the cylinder cavity, the static liquid piston includes a piston face configured to carry liquid piston fluid; and wherein the reciprocating cylinder is configured to move relative to the static liquid piston between contracted and expanded positions to compress a compressible fluid: in the expanded position the cylinder head is withdrawn from liquid piston fluid and the cylinder cavity is filled with the compressible fluid, and in the contracted position the cylinder head is near the liquid piston fluid and the compressible fluid is compressed.
 2. The system of claim 1 comprising liquid piston fluid carried on the piston face.
 3. The system of claim 2, wherein the liquid piston fluid includes a liquid piston ferrofluid, and the static liquid piston includes a retention magnet configured retain the liquid piston ferrofluid along the piston face.
 4. The system of claim 2, wherein liquid piston fluid is a heat sink or heat source.
 5. The system of claim 4, wherein the compressor assembly includes a heat exchanger in communication with the liquid piston fluid, and the heat exchanger is configured to extract heat from the liquid piston fluid heated by the compressed compressible fluid.
 6. The system of claim 5 comprising a compressible fluid, and the compressible fluid is isothermal between the expanded and contracted positions according to the liquid piston fluid heat sink and the operation of the heat exchanger.
 7. The system of claim 1, wherein the reciprocating cylinder includes a porous heat transfer media within the cylinder cavity.
 8. The system of claim 7, wherein the porous heat transfer media consists of one or more of tubes, posts, fins, interlaced tubes, interlaced posts, interlaced fins, tilted interrupted plates, profiled cylinder cavity walls, metallic foam or wire mesh.
 9. The system of claim 7, wherein the porous heat transfer media includes a phobic coating with respect to the liquid piston fluid.
 10. The system of claim 1, wherein the compressor assembly includes one or more spray ports configured to spray a heat sink fluid into the cylinder cavity.
 11. The system of claim 10 comprising liquid piston fluid housed on the piston face, and the sprayed heat sink fluid is the same as the liquid piston fluid.
 12. A liquid piston compressor assembly comprising: a reciprocating cylinder including a cylinder cavity and a cylinder head; a static liquid piston received in the cylinder cavity, the static liquid piston includes: a piston face, a liquid piston ferrofluid along the piston face, and a retention magnet; and wherein the reciprocating cylinder is configured to move relative to the static liquid piston between contracted and expanded positions: in the expanded position the cylinder head is withdrawn from the liquid piston ferrofluid, in the contracted position the cylinder head is near the liquid piston ferrofluid, and the retention magnet is configured to retain the liquid piston ferrofluid along the piston face in each of the expanded and contracted positions and during movement therebetween.
 13. The assembly of claim 12, wherein the liquid piston ferrofluid includes a liquid base and a plurality of ferrous particles suspended in the liquid base.
 14. The assembly of claim 13, wherein the liquid piston ferrofluid includes a surfactant.
 15. The assembly of claim 12, wherein the reciprocating cylinder includes a porous heat transfer media within the cylinder cavity.
 16. The assembly of claim 15, wherein the retention magnet is configured to extract the liquid piston ferrofluid from interstitial locations of the porous heat transfer media with movement of the reciprocating cylinder between the contracted and expanded positions.
 17. The assembly of claim 12 comprising a heat exchanger in communication with the liquid piston ferrofluid, wherein the heat exchanger is configured to extract heat from the liquid piston ferrofluid, the liquid piston ferrofluid heated by compression of a compressible fluid with movement of the reciprocating cylinder between the expanded and contracted positions.
 18. The assembly of claim 25, wherein the compressible fluid is isothermal between the expanded and contracted positions according to the liquid piston ferrofluid and the operation of the heat exchanger.
 19. A method of using a liquid piston compressor system comprising: introducing a compressible fluid at a first temperature to a cylinder cavity of a reciprocating cylinder in an expanded position: isothermally compressing the compressible fluid within the cylinder cavity, compressing including: moving the reciprocating cylinder toward a contracted position relative to a static liquid piston to compress the compressible fluid, and extracting heat from the compressible fluid, the heat generated with compression of the compressible fluid; and evacuating the compressed compressible fluid from the cylinder cavity at a second temperature near the first temperature.
 20. The method of claim 19, wherein the static liquid piston includes liquid piston fluid, and extracting heat from the compressible fluid includes: transferring heat from the compressible fluid to material of the reciprocating cylinder, transferring heat to the liquid piston fluid from the material of the reciprocating cylinder, cycling the heated liquid piston fluid through a heat exchanger, and extracting heat from the liquid piston fluid at the heat exchanger.
 21. The method of claim 20, wherein the material of the reciprocating cylinder includes a porous heat transfer media, and transferring heat from the compressible fluid to the material of the reciprocating cylinder includes transferring heat to a porous heat transfer media within the reciprocating cylinder in intimate contact with the compressible fluid during isothermal compression, and transferring heat to the liquid piston fluid includes transferring heat from the porous heat transfer media to the liquid piston fluid in intimate contact with the porous heat transfer media at least in the contracted position.
 22. The method of claim 21, wherein moving the reciprocating cylinder toward the contracted position relative to the static liquid piston includes infiltrating the porous heat transfer media with the liquid piston fluid.
 23. The method of claim 19, wherein extracting heat from the compressible fluid includes: spraying a heat sink fluid into the reciprocating cylinder, extracting heat from the compressible fluid with the sprayed heat sink fluid, and mixing the heated sprayed heat sink fluid with the liquid piston fluid according to settling of the heated sprayed heat sink fluid.
 24. The method of claim 19, wherein isothermally compressing the compressible fluid includes reciprocating the reciprocating cylinder relative to the static liquid piston at an operating frequency that decelerates the reciprocating cylinder at a deceleration greater than one gravity.
 25. The method of claim 19, wherein the static liquid piston includes a liquid piston fluid along a piston face and comprising retaining the liquid piston fluid along the piston face.
 26. The method of claim 25, wherein the liquid piston fluid includes a liquid piston ferrofluid, and retaining the liquid piston fluid along the piston face includes biasing the liquid piston ferrofluid toward the piston face with a retention magnet.
 27. The method of claim 26, wherein the reciprocating cylinder includes a porous heat transfer media, and retaining the liquid piston fluid along the piston face includes extracting the liquid piston ferrofluid from interstitial locations within the porous heat transfer media according to biasing of the liquid piston ferrofluid toward the piston face at least during retraction of the reciprocating cylinder from the contracted position.
 28. The method of claim 26, wherein retaining the liquid piston fluid along the piston face includes biasing the liquid piston ferrofluid toward a moving interface between the reciprocating cylinder and the piston face. 